The present invention relates to a heat exchanger which is used in an air-conditioner, a refrigerator or the like and indirectly effects transfer of heat between two fluids.
As shown in FIG. 1, a conventional heat exchanger of this type comprises heat transfer tubes 2 made of copper or the like and connected to each other by means of U-bends, fins 1 made of aluminum or the like, and so forth, wherein heat exchange is carried out by a fluid passing through the tubes 2 and air which flows among fins 1 in the direction of the arrow.
Such a heat exchanger has come to be required to be compact and to possess high performance. However, in view of such problems as noise, the rate of flow among the fins 1 is restrained to a low level, and, as compared with the heat resistance of the tube interior side, the heat resistance of the fin surfaces side is extremely high. For that reason, a difference in heat resistance between both sides is reduced by expanding the areas of the fins 1. Nevertheless, there are limits to expanding the surface areas of the fins 1, and, at present, the heat resistance of the fin surface side is still substantially greater than the heat resistance of the tube interior side.
For this reason, in recent years, an attempt has been made to reduce the heat resistance between air and the fins by working on the fin surfaces.
FIG. 2 is a top plan view of a conventional example of improvement. In the drawing, reference numeral 1 denotes a fin; 2, a heat transfer tube; and 3, a fin base. Reference numerals 105, 106, 115, 116, 125 and 126 denote rising portions; 107, 117 and 127, transverse portions; and 104, 114 and 124, cutouts. Reference character R denotes a gas passage; A, air; and l, a center line of an air passage.
The heat exchanger shown in FIG. 2 uses the fin 1 in which the cutouts 104, 114 and 124 formed by causing the transverse portions 107, 117 and 127 to span the pairs of the rising pieces 105 and 106, 115 and 116, and 125 and 126 across the air passage R between fin collars 12 for the heat transfer tubes 2 which are disposed adjacent to each other. The cutouts 104, 114 are disposed on the air flow inlet side and the air flow outlet side, and are separated from each other in the direction of a row thereof. On the other hand, the cutouts 104 are disposed between the aforementioned two sides and are not divided. Further, the angle of inclination of the rising portions 105, 106, 115, 125 of the cutouts 104, 114, 124 on the heat transfer tube 2 side is set in such a manner as to surround the outer peripheries of the respective heat transfer tubes 2, while the remaining rising pieces 116, 126 have an angle of inclination with respect to the center line l of the air passage. At the same time, between the cutouts 114, 124 on the air flow inlet side and the cutouts 114, 124 on the air flow outlet side, the directions of inclination of the rising pieces 116, 126 are arranged to be opposite to each other. As the air flows along these rising portions 116, 126, the mixing of the air A passing through the air passage R is accelerated, so that it is possible to improve the heat exchange efficiency.
However, the effect of mixing the air A in the finned heat exchanger using the fins shown in FIG. 2 is not derived from only the fact that the air flows along the rising portions 116, 126, so that it has not been possible to improve the heat exchange efficiency remarkably.
The above-described arrangement is disclosed in Japanese Utility Model Unexamined Publication No. 57-139086.
There have been proposed many improvements to enhance the efficiency of the heat exchanger other than the above-described one, and some of them will be described below.
For instance, Japanese Patent Examined Publication No. 59-26237, Japanese Patent Unexamined Publication No. 61-217695 and Japanese Utility Model Unexamined Publication No. 62-34676 disclose an arrangement in which rectangular cutouts are arranged under a certain condition. In addition, Japanese Utility Model Examined Publication No. 62-38152 discloses an arrangement in which trapezoidal cutouts having different sizes and equal legs are arranged.
However, with the former arrangement, since the rising portions of the cutouts project parallel with the direction of the air flow, the action of disturbing the air flow passing among the fins is lacking, so that it is impossible to expect an effect of improving the heat transfer capabilities based on the action of turbulence.
On the other hand, with the latter arrangement, since all the adjacent rising portions are located parallel with each other, it is possible to vary the direction of the air flow, but the action of disturbing the air flow is small, so that it is still impossible to expect the effect of improving the heat transfer capabilities based on the action of turbulence.